According to the related art, optical communication systems that use wavelength division multiplexing (WDM) are known (hereafter, WDM communication systems). With WDM communication systems, transmitting wavelength multiplexed signaling light in which signaling light of multiple wavelengths is multiplexed enables different information to be transmitted simultaneously. Further, the wavelength multiplexed signaling light is called WD signaling light.
Regarding WDM communication systems, optical switches, which are so-called wavelength selectable switches, are provisioned in the optical transmission devices on the network to transmit the multiple streams of information to the desired output destinations. For example, the wavelength selectable switch, which includes an light reflection unit in which the reflection direction is changeable, modifies the reflection direction of the light reflection unit, and optically connects an arbitrary input port which receives input of the WDM signaling light to an arbitrary output port via the light reflection unit. As a result, the wavelength selectable switch generates the WDM signaling light by multiplexing the received signaling light, and divides the signaling light of an arbitrary wavelength from the signaling light that has been multiplexed into WDM signaling light.
The wavelength selectable switch according to the related art will be described using FIGS. 40 and 41. FIG. 40 is a cross-sectional diagram of the wavelength selectable switch according to the related art, and FIG. 41 is a top view diagram of the wavelength selectable switch according to the related art. Further, regarding FIGS. 40 and 41, the solid lines represent the optical path of the signaling light, and the bidirectional arrows represent the direction of movement.
As illustrated in FIG. 40, the wavelength selectable switch includes, for example, multiple input ports that receive the input signaling light and multiple output ports that output the signaling light. The wavelength selectable switch also includes a first optical system which includes a lens and such to collimate the signaling light input from the input port and the signaling light output from the output port.
As illustrated in FIG. 41, when WDM signaling light, which is the signaling light multiplexed with an m type of wavelengths λ1 through λm, is input into the wavelength selectable switch, the wavelength selectable switch collimates the WDM signaling light input from the input port at the first optical system, and then illuminates a wavelength division unit. Then, a second optical system condenses signaling light divided for each wavelength, illuminates this to a micro electro mechanical system (MEMS) array with an m number of MEMS mirrors provisioned corresponding to each wavelength. The m number of micro electro mechanical system (MEMS) mirrors are an example of the light reflection unit that may change the reflection direction.
Here, the MEMS array rotationally drives the MEMS mirror along the X axis to change the reflection direction of the MEMS mirror, and optically connects the arbitrary input port that receives the input WDM signaling light and the arbitrary output port via the MEMS mirror. The reflection direction of the MEMS mirror may be changed, for example, by applying drive voltage to an electrode to rotationally drive the MEMS mirror, and then using the electrostatic force generated by the electrode.
Then, the wavelength selectable switch collimates the signaling light reflected by the MEMS mirror in which the reflection direction has been changed at the second optical system, and outputs this from an optional output port via wavelength division. Further, the wavelength selectable switch may be set to output at an optional damping rate for each wavelength by rotationally driving the MEMS mirror along the X axis or Y axis in very fine increments.
Although the wavelength selectable switch including multiple input and output ports has been described using FIGS. 40 and 41, other known switches include a DROP type wavelength selectable switch with one input port and multiple output ports, and an ADD type wavelength selectable switch with multiple input ports and only one output port.
An example of the related art is disclosed in Japanese Laid-open Patent Publication No. 2006-267522.
The wavelength selectable switch previously described unfortunately has not been given enough consideration to suitable determination of light reflection unit malfunctions.
Specifically, regarding the wavelength selectable switch according to the related art, when the MEMS mirror malfunctions due to some reason and is not rotationally driven, the signaling light reflected on the MEMS mirror will not be output from the output port, and the monitor value of the light output from the output port is zero. When the monitor value of the light output from the output port is zero, a malfunction may have occurred in the MEMS mirror, or a malfunction may have occurred in a monitor device which is provisioned downstream from the output node, or a malfunction may have occurred in a node upstream from the wavelength selectable switch. However, the wavelength selectable switch according to the related art does not differentiate between and determine whether a malfunction has occurred in the monitor device which is provisioned downstream from the output node, a malfunction has occurred in the node upstream from the wavelength selectable switch, or a malfunction has occurred in the MEMS mirror. For this reason, it is difficult for a MEMS mirror malfunction to be properly determined at the wavelength selectable switch according to the related art.
Thus, a method to determine that a malfunction has occurred in the MEMS mirror may be implemented by measuring the voltage applied to the electrode of the MEMS mirror and then comparing the measured voltage value with a target value. However, with this method, an electronic part for measuring the voltage applied to the electrode of the MEMS mirror is provisioned to each MEMS mirror, and this may cause the device to become increasingly larger as the number of MEMS mirrors increase. For this reason, the method to measure the voltage applied to the electrode of the MEMS mirror is not very realistic.